1. Field of the Invention
The present invention relates to a screw fastening device which automatically fastens a screw by operation of a robot, etc.
2. Description of the Related Art
A nut runner is used to detect fastening torque and controls torque for the purpose of improving the reliability of machinery and structures. Japanese Examined Utility Model Publication No. 63-46232U discloses a nut runner which is provided with a torque detector.
Furthermore, Japanese Patent Publication No. 2010-012583A discloses a device which is provided with a fastening operation monitoring means for monitoring a fastening operation force when a hand of a robot fastens a wrench.
A general nut runner such as disclosed in Japanese Examined Utility Model Publication No. 63-46232U uses a built in motor to turn the front end of a tool which is arranged on its axis. For this reason, a relatively large space is considered necessary in front of the nut etc. to be fastened. If such a space cannot be secured, it is necessary to build an offset gear etc. inside the nut runner.
However, since such a gear is used for transmitting a torque, it is difficult to make the gear small in size. For this reason, the nut runner with such a built-in gear tends to become large in size as a result. Further, when the above-mentioned space cannot be secured, it is necessary to lower the upper limit of the fastening torque. Further, automation of the nut runner itself is difficult.
Furthermore, the fastening operation monitoring means which is disclosed in Japanese Patent Publication No. 2010-012583A is a strain gauge, so there is also the problem that the cost of the device as a whole becomes high.
The present invention was made in consideration of this situation and has as its object to provide an inexpensive screw fastening device which can automate the fastening work even when only a limited space can be secured.